Washington -LRB- CNN -RRB- A year after ISIS became a household name in America , using brutality and savvy propaganda to challenge al Qaeda and its affiliates for jihadist adherents , U.S. prosecutions of would-be recruits have exploded .

The flurry of arrests -- at least 25 people have been detained since January -- is a sign that complicated , manpower-intensive investigations begun when ISIS started seizing swaths of territory a year ago are finally being completed .

But they also highlight the unique challenges that ISIS poses in comparison with al Qaeda , which has attracted fewer U.S.-based recruits .

Like a new rock band storming the music charts , ISIS has benefited from a media environment that amplifies its propaganda , law enforcement officials said . The group quickly reached early recruits through videos that showcased the fear its adherents instilled in nonbelievers .

At first , most of the recruits were self-starters -- people radicalized on their own from consuming ISIS propaganda from YouTube videos and other social media . Much of the propaganda comes in the form of slick movie trailer-style videos , some glorifying brutal practices such as the beheading of anyone who ISIS leaders decide does n't comport with their medieval brand of Islam .

But once those initial Western recruits arrived , living in the self-declared ISIS caliphate spanning parts of Syria and Iraq , they started to directly entice friends and other contacts back home to join them .

In Minnesota , nine men have been charged as part of an alleged cell of recruits linked to American Abdi Nur , who turned up fighting with ISIS in Syria in 2014 and began to appeal to his friends to come to the Middle East .

`` Each one of those folks who makes it over there has the capability to reach out back to their contacts back here , '' a senior U.S. counterterrorism official said .

It 's a phenomenon observed in Norway and other European nations , where clusters of young people have been lured to ISIS .

And the ISIS recruiters have an easier path to drawing supporters than al Qaeda has had . A decade ago , that group 's recruits faced formidable obstacles trying to get to training camps deep in hard-to-reach areas of Afghanistan and Pakistan 's tribal region . Few Westerners went through the trouble .

Minneapolis men allegedly trying to join ISIS highlight role of American recruiter

Today , ISIS occupies much more accessible territory , mostly reachable through Turkey . Istanbul 's airport has easy connections to Western Europe and much of the rest of the world . From there , Turkey 's modern infrastructure offers quick access to the border regions where smugglers can help jihadis get across to Syria .

The informal recruitment networks and ease of travel have presented a difficult puzzle to intelligence and counterterrorism officials , who are used to tracking networks of facilitators and fundraisers that funnel recruits eastward .

`` It 's harder for us to pick up on , '' the U.S. counterterrorism official said of the peer-to-peer recruitment , which is well below the radar .

How ISIS is luring Westerners

Before ISIS , investigators could often focus on radicalizing mosques and clerics to figure out those networks .

Al Qaeda recruitment focused on attracting radicals who were motivated to join the fight to protect Islamic holy lands . Much of the recruitment occurred in countries with strong conservative Islamic histories , including Saudi Arabia and Yemen , U.S. officials said .

In contrast , ISIS takes a somewhat secular approach , portraying how much better life purportedly is in the caliphate as compared to the corrupt West . And people attracted to ISIS ' marketing run the gamut from rich to poor , educated to dropout , male to female , teenaged to middle-aged .

There are signs Western recruits have risen to high levels in the ISIS organization , with their influence reflected in the latest propaganda , counterterrorism and intelligence officials said . The English is proper , with fewer grammatical and spelling mistakes .

And while the large number of arrests show that law enforcement officials are succeeding in their disruption efforts , it also means that U.S. authorities do n't see the lure of ISIS receding any time soon .

`` We are opening cases quicker than we are closing them , '' the U.S. counterterrorism official said .

Who has been recruited to ISIS from the West ?

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The recruiting tactics used by ISIS differ from those traditionally employed by al Qaeda

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ISIS benefits from a media environment that amplifies its propaganda , officials say